Loans and Leases and the Allowance for Credit Losses - Loan Modification Activities that were Considered Troubled Debt Restructurings (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2017 USD ($) Modification	Mar. 31, 2016 USD ($) Modification
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	168	219
Pre-modification recorded investment	$ 44,692	$ 34,904
Post- modification	$ 39,892	$ 36,143
Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	20	21
Pre-modification recorded investment	$ 6,702	$ 7,416
Post- modification	6,597	7,372
Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	13,647	19,728
Principal Deferral [Member] | Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	2,991	3,448
Other [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	1,297	63
Combination of Concession Types [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	24,948	16,352
Combination of Concession Types [Member] | Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	$ 3,606	$ 3,924
Commercial, Financial, Leasing, etc. [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	50	31
Pre-modification recorded investment	$ 11,921	$ 17,728
Post- modification	7,923	18,673
Commercial, Financial, Leasing, etc. [Member] | Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	4,389	12,721
Commercial, Financial, Leasing, etc. [Member] | Other [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	806
Commercial, Financial, Leasing, etc. [Member] | Combination of Concession Types [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	$ 2,728	$ 5,952
Residential Builder and Developer [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	3
Pre-modification recorded investment	$ 12,291
Post- modification	10,879
Residential Builder and Developer [Member] | Combination of Concession Types [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	$ 10,879
Other Commercial Construction [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	1
Pre-modification recorded investment	$ 102
Post- modification	102
Other Commercial Construction [Member] | Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	$ 102
Residential [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	41	27
Pre-modification recorded investment	$ 9,380	$ 4,302
Post- modification	9,948	4,560
Residential [Member] | Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	5,593	2,191
Residential [Member] | Combination of Concession Types [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	$ 4,355	$ 2,369
Residential Limited Documentation [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	6	6
Pre-modification recorded investment	$ 1,378	$ 1,437
Post- modification	1,525	1,517
Residential Limited Documentation [Member] | Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification		138
Residential Limited Documentation [Member] | Combination of Concession Types [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	$ 1,525	$ 1,379
Home Equity Lines and Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	25	26
Pre-modification recorded investment	$ 2,502	$ 2,831
Post- modification	2,502	2,831
Home Equity Lines and Loans [Member] | Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	163	335
Home Equity Lines and Loans [Member] | Other [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	491
Home Equity Lines and Loans [Member] | Combination of Concession Types [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	$ 1,848	$ 2,496
Automobile [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	20	72
Pre-modification recorded investment	$ 390	$ 644
Post- modification	390	644
Automobile [Member] | Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	383	521
Automobile [Member] | Other [Member]
Financing Receivable, Modifications [Line Items]
Post- modification		38
Automobile [Member] | Combination of Concession Types [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	$ 7	$ 85
Other [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	2	36
Pre-modification recorded investment	$ 26	$ 546
Post- modification	26	546
Other [Member] | Principal Deferral [Member]
Financing Receivable, Modifications [Line Items]
Post- modification	$ 26	374
Other [Member] | Other [Member]
Financing Receivable, Modifications [Line Items]
Post- modification		25
Other [Member] | Combination of Concession Types [Member]
Financing Receivable, Modifications [Line Items]
Post- modification		$ 147